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| + | #REDIRECT[[:Category:Nematodes]] |
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| − | |linkpage =Parasites
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| − | |linktext =PARASITES
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| − | <br>
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| − | == Introduction ==
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| − | Nematodes are one of the most prolific life-forms on this planet. Most are free-living, with species adapted to every imaginable habitat. Some are parasitic on plants, and others on animals. The animal parasitic nematodes form a large and diverse array of organisms.
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| − | == The Nematodes ==
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| − | === Recognition Features ===
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| − | *A unique feature of the nematodes is that the fluid in the body cavity is maintained under high pressue (this is why nematodes often burst after collection).
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| − | *They therefore have a tough elastic cuticle which often forms elaborate structures useful for identification.
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| − | *A muscular pharynx is needed to pump food into the intestine.
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| − | *The shape of the pharynx is characteristic in some groups.
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| − | *There is a nerve ring around the pharynx and four longitudinal nerves with ganglia that co-ordinate movement (many anthelmintics act by disrupting neuromuscular co-ordination).
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| − | *The sexes are separate:
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| − | **the female tail generally ends in a blunt point
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| − | **males usually have two chitinous rods that can be protruded through the cloaca to hold the female - these are called spicules and, being chitinous, are easily seen under the microscope. As they differ in shape and size between species, they are very useful for identification.
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| − | *The '''bursate nematodes''' are characterised by a large expansion of the cuticle of the male tail to form a clasping organ (the bursa).
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| − | *Other modifications of the cuticle on both male and female nematodes useful for identification include:
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| − | **'''alae''' (wing-like protrusions)
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| − | **'''vesicles''' (swellings around the whole circumference of the body).
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| − | *The heads of some nematodes have structures such as:
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| − | **leaf-like lips around the mouth (the '''leaf-crown''')
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| − | **a '''buccal cavity'''
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| − | **'''teeth''' or '''cutting plates'''.
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| − | === Feeding Habits ===
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| − | *Many intestinal nematodes are closely applied to the mucosal surface.
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| − | *Some swallow ingesta and/or host secretions.
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| − | *Others suck a plug of mucosa into the buccal cavity (plug feeders), leaving a circular ulcer.
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| − | *Yet others bury their heads deep into the mucosa and suck blood.
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| − | === General Life-Cycle ===
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| − | *The basic life-cycle is very simple:
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| − | egg → L1 → L2 → L3 → L4 → adult
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| − | *With a moult in between each larval stage.
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| − | *But there are many variations on this theme!
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| − | === Nematode Eggs ===
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| − | These vary greatly in appearance and are very useful for diagnosis as they can often be detected and counted in faecal samples.
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| − | NOTE: we use the typical '''strongyle''' egg to provide us with a yard-stick for comparing sizes. A "large egg", for example, means larger than a strongyle egg. A typical strongyle egg is approximately '''80µm''' long.
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| − | == Nematode Superfamilies ==
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| − | '''BURSATE'''
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| − | *[[Trichostrongyloidea]]
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| − | *[[Strongyloidea]]
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| − | *[[Ancylostomatoidea]] (Hook worms)
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| − | *[[Metastrongyloidae]]
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| − | NOTE: the Trichostrongyloidea, Strongyloidea and hookworms are very closely related, and are often collectively known as '''"the strongyles"'''. Typically, they produce almost identical eggs, called '''"typical strongyle eggs"'''.
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| − | '''NON-BURSATE'''
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| − | *[[Ascaridoidea]]
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| − | *[[Oxyuroidea]]
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| − | *[[Rhabditoidea]]
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| − | *[[Trichinelloidea]]
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| − | *[[Spiruroidea]]
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| − | *[[Filarioidea]]
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| − | From the veterinary view-point, the nematodes are most conveniently grouped into '''superfamilies''' because their members often have similar life-cycles and epidemiological features. Superfamily names end in -oidea (the anglicised form is -oid, as in trichostrongyloid).
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| − | Occlusion of pancreatic ducts sometimes happens [[Pancreas Parasitic - Pathology]]
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